Insulin signaling is an evolutionarily conserved mechanism used by multi-cellular organisms to regulate metabolism, growth, and lifespan. While the signaling pathways triggered by insulin are well characterized, there are still gaps in our understanding of the mechanisms that modulate insulin action and how they might be impaired in diseases such as type 2 diabetes. Insulin degrading enzyme (IDE) was discovered over a decade ago to be a major cellular protease that degrades insulin in vitro, yet an understanding of the role that IDE plays in regulating insulin in vivo has been limited. The more recent finding that IDE degrades the amyloid beta peptides of Alzheimer's disease has fueled further interest in this protease. I recently initiated genetic analysis of IDE function in Drosophila, which has a single gene encoding the likely ortholog of human IDE. My preliminary studies provocatively suggest that IDE is involved in physiological processes known to involve insulin signaling but may also have a novel role in tissue morphogenesis. The overall goal of this proposal is to define the biological roles of IDE and in particular to test whether IDE is a physiological regulator of insulin signaling. This goal will be addressed with the following specific aims. The first aim of this proposal is to determine if IDE is expressed in brain neurosecretory cells that secrete insulin-like peptides. RNA in situ hybridization and immunolocalization experiments will be performed to determine the tissue distribution of IDE, in particular to test if IDE is expressed in brain neurosecretory cells that secrete insulin-like peptides (DILPs). The second aim is to test if IDE can antagonize the biological activity of insulin-like peptides. IDE and DILPs will be co-expressed in Drosophila tissues to assess whether IDE can block the cellular growth promoting activity of DILPs, as would be predicted if IDE degrades DILPs. The third aim of this study is to investigate the role of IDE in physiological processes involving insulin signaling. Gain-of-function and loss-of-function analysis will be performed to investigate the role of IDE in processes involving insulin signaling, specifically lifespan determination and regulation of growth and metabolism. Whether a loss-of-function IDE phenotype is suppressed by reducing DILP activity will be used as a critical genetic test of the hypothesis that a physiological role of IDE is to degrade DILPs. Finally, the role of IDE in tissue morphogenesis will be elucidated. Preliminary studies suggest that IDE is involved in adult thorax development, which may not involve insulin signaling. Genetic analysis will be used to address whether IDE is important for viability of cells that give rise to thorax structures or whether it interacts with the TGF-P signaling pathway required for thorax patterning.